Changes in central fatigue have been linked to active and passive changes in core temperature as well as integration of sensory feedback from thermoreceptors in the skin. However, the effects of muscle temperature (Tm), and thereby metaboreceptor and local afferent nerve temperature, on central fatigue (measured using voluntary activation percentage) during sustained, high muscle fatigue exercise remain unexamined. In this study, we investigated Tm across the range of cold to hot, and its effect on voluntary activation percentage during sustained isometric contractions of the knee-extensors. The results suggest that contrary to brief contractions, during a sustained fatiguing contraction Tm significantly (p < 0.001) influences force output (-0.7% per-degree-centigrade increase) and central fatigue (-0.5% per-degree-centigrade increase) showing a negative relationship across the Tm continuum in moderately trained individuals. The negative relationship between voluntary activation percentage and Tm indicates muscle temperature may influence central fatigue during sustained and high muscle fatigue exercise. Based on an integrative analysis between the present data and previous literature, the impact of core and muscle temperature on voluntary muscle activation is estimated to show a ratio of 5.5 to 1 respectively. Accordingly, Tm could assume a secondary or tertiary role in the reduction of voluntary muscle activation when body temperature leaves a thermoneutral range.